Female Myotis lucifugus lucifugus, obtained from a hibernaculum in northern central Ontario, were aroused during the week that normal departures from hibernation began, maintained in large cages at 28–30°C, and fed mealworms daily. Some bats ovulated less than 24 hr after arousal, and with one exception, all bats with normal, mature follicles ovulated within 72 hr. Histological examination of reproductive tracts from ovulated bats indicated that oviductal transit was completed in 24–48 hr, and that blastocyst formation and implantation occurred 4 and 10 days, respectively, after fertilization. These time intervals were somewhat shorter than those reported in previous studies; however, the differences appeared to be due to the relative accuracy in determining the time of ovulation, not to differences in rates of development among different populations.